1. Field of the Invention
The invention relates to an indicating instrument for a vehicle having an analog indication of a currently measured value and having a variable indication of a reference value.
2. Description of the Related Art
Indicating instruments which include an analog indication of a currently measured value and a variable indication of a reference value are constructed, for example, as barometers for determining the air pressure. Barometers have a pointer which may be rotated by hand so that a user can set the pointer to the current air pressure. After some time, the user can then determine whether the air pressure has risen or fallen by comparing the current air pressure to the pointer. Tachometers for tractors may also be configured with a settable pointer. As a result, the driver may, for example, set the pointer to mark the optimum travel speed for a plough during a ploughing operation. Once the pointer is set, deviations from the optimum travel speed strike the driver more clearly than if the driver had only to note the correct speed.
In a vehicle, critical reference variables often vary with operating conditions. For example, drivers of motor vehicles know that when an internal combustion engine is still cold, the engine should be driven at a lower engine speed than when the engine is at operating temperature. However, it is not clear which maximum engine speed may actually be used during the warming-up phase of the internal combustion engine.
Furthermore, the reference speed of a tachometer or a speedometer of a motor vehicle changes very frequently while driving. For example, the reference speed is typically a maximum of 50 km/h in built-up areas and is 100 km/h on open roads. Many different reference speeds may additionally depend on different speed limitations in congested areas such as towns and cities. Therefore, upon detecting a speed limit, the driver could mark this on his speedometer by manually adjusting a reference pointer just as the reference pointer of a barometer is set. However, this would be tiresome and has the risk of being wrongly implemented in view of the very many and frequently changing speed limitations which can often not be comprehended logically.
It is an object of the present invention to construct an indicating instrument including a variable indication of a reference value such that changes in the reference value may be taken into account with minimal burden on the user.
According to the invention, the object is met by an automatic setting device for the indicator of the reference value in response to variable data which are significant for the indicated measured variable.
The indicating instrument according to the present invention includes a reference indication value which is always shown in addition to the current indication value and which varies automatically in accordance with the requirements. The indicating instrument according to the present invention allows a user to control a system or a vehicle in such a way that a reference value to be complied with in each case is observed. Since the reference value is automatically adapted to the requirements, the viewer does not need to set any reference values or to note them. The indicating instrument according to the invention may be used in various types vehicles to comply with a reference speed. For example, ships and aircraft have a fixed arrival time and an optimum speed for the fuel consumption. Railborne vehicles are subject to different reference speeds for different sections of the railroad.
The indicating instrument may comprise a revolution counter and the setting device for adjusting the reference value may operate on the basis of operating data from the internal combustion engine of the vehicle. Conventional revolution counters typically mark in red the engine speeds which must not be exceeded or may be exceeded only briefly when the internal combustion engine is operating normal at the operating temperature. However, a revolution counter according to the present invention may variably indicate a maximum speed such that the maximum value is low when the internal combustion engine is cold and rises as the internal combustion engine warms up. The variable maximum value reference ensures that the driver drives in a non-damaging way, even under unfavorable operating conditions.
A revolution counter according to the present invention is constructed particularly simply for the application in the vehicle if the setting device for adjusting the reference value operates in response to the oil temperature of the internal combustion engine in the vehicle.
In a specific embodiment of the present invention, the indicating instrument comprises a speedometer and the setting device is designed to adjust the reference value on the basis of the position of the vehicle. According to this embodiment, the driver no longer needs to pay attention to road signs such as place name signs and speed limit signs to comply with the speed limit existing in built-up areas Instead, the reference speed changes after the passing of a road sign is automatically signaled to his tachometer on the basis of his vehicle position so that the driver can very rapidly recognize whether he is too fast or unnecessarily slow on the basis of the angular difference between the speedometer pointer and the indication of the reference value.
The necessary setting commands depending on the vehicle position may be obtained very cost-effectively when the setting device is designed to adjust to the reference value in response to setting commands from a vehicle navigation system. The navigation system already includes information regarding the respective localities on the basis of stored road maps. Furthermore, the location system of the navigation system knows where the vehicle is currently located. Accordingly, the addition of a control for the indication of the reference value necessitates only minimal additional outlay when an existing navigation system is used to control the indication of the reference value.
In an alternative embodiment, the setting device is designed to adjust the reference value in response to external data transmitted wirelessly. For example, the variable speed limits which are common on freeways for controlling the traffic flow may be broadcast by radio so that the variable reference value on the indicating instrument could be controlled on the basis of such radio signals.
Even without detection of vehicle position and without radio transmission of information, the indication of the reference value could be controlled by the setting device for adjusting the reference value operating by automatic image recognition of traffic signs.
The indicating instrument of the present invention may include a manual bypass to override the automatic setting. The driver may use this option of setting a reference value indication by manually inputting in addition to the automatic input. This embodiment is required, for example, when a heavy goods vehicle is temporarily being used with a trailer and has to comply with the speed limit prescribed for that use.
A deviation from the reference value may be easily recognized by a driver when the setting device is designed to rotate the indicating instrument into a position in which the pointer is horizontal or vertical when there is agreement between the current measured value and the reference value. Experience shows that the eye detects deviations from the horizontal or vertical particularly quickly.
To illustrate the deviation from a reference value, means for the differently colored illumination of at least of the sector between the pointer indicating the current measured value and the reference value may be provided. The color of the sector between the pointer and the reference value may be designed to depend on whether the measured value falls above or below the reference value.
Other objects and features of the present invention will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for purposes of illustration and not as a definition of the limits of the invention, for which reference should be made to the appended claims. It should be further understood that the drawings are not necessarily drawn to scale and that, unless otherwise indicated, they are merely intended to conceptually illustrate the structures and procedures described herein.